The CAS Registry Mumber 25751-28-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,5,7,5 and 1 respectively; the second part has 2 digits, 2 and 8 respectively. Calculate Digit Verification of CAS Registry Number 25751-28: (7*2)+(6*5)+(5*7)+(4*5)+(3*1)+(2*2)+(1*8)=114 114 % 10 = 4 So 25751-28-4 is a valid CAS Registry Number.